In recent years, the demands on the manufacturing industry have undergone significant changes, particularly in the area of development and prototype manufacturing. As product variants are becoming steadily more numerous and complex, so the need for prototypes is also growing constantly. Many new technologies have emerged, which are described by the umbrella term “rapid prototyping” or “rapid manufacturing” and are used to meet the demand for more flexible manufacturing.
An significant feature of these processes is the creation of process control data from CAD geometry data with subsequent control of processing facilities. All such processes share the following features. Shaping is carried out not by removing material, but by adding material, or by phase transition of a material from liquid to solid, or a starting material in powder form is compacted. Moreover, all methods are based on part geometries from layers of finite thickness, which are built up directly from CAD data using a slice process.
The methods currently available differ in respect of the initial state of the materials, that is to say solid, liquid or gas-phase, in which the layer addition or construction process takes place. In the following, various methods will be discussed.
Selective Laser Sintering (SLS) was originally developed for powders consisting of nylon, polycarbonate and waxes, and was later applied to metal powders. Powder layers are sintered onto a green body in a reactor, wherein the melting temperature is reached through the use of CO2 lasers.
In Multiphase Jet Solidification (MJS), mixtures of metal powder and binder are processed in a manner similar to the injection moulding method by computer-controlled, movable nozzles to form layers, which in turn build the component.
Stereolithography uses liquid UV-sensitive polymers as starting materials; the polymers are cured by laser radiation one layer at a time and deposited on the substrate. The workpiece is built progressively on a platform that descends by the corresponding layer thickness after the respective layer has cured in the resin bath.
Liquid polymers are also used as the raw materials in Solid Ground Curing (SGC). Thin polymer layers harden after exposure to UV radiation at the desired locations and thus build a component one layer at a time.
Simultaneous shot peening (SSP) is the name for a method in which the surface of a suitable form is mapped by spraying with molten metal. This mapping can be used as part of a die casting tool or press form.
Very similar to the MJS process is Fused Deposition Modeling (FDM). Here too, a nozzle is controlled using NC as it travels over the height-adjustable workpiece that is to be made. The component is built by cutting away molten material layer by layer and lowering the platform correspondingly.
Laminated Object Manufacturing (LOM) was originally developed for manufacturing paper or plastic components. A laser cuts the corresponding component layers out of individual layers, and these are laminated together using adhesives to create the workpiece.
Document EP 1,266,878 describes an “LSD method” and a device for carrying out the method, in which ceramic green sheets are applied using a process derived from tape casting. After this, and similarly to Selective Laser Sintering, a laser is used to harden/sinter specific areas of the ceramic green sheets. The moulded body is built up in layers by sintering selected areas of the ceramic material with the laser beam. In the known method, layers of a liquid suspension or a plastic mass are applied repeatedly and then dehumidified. Each dehumidified layer is then sintered at selected locations using the laser beam at selected locations to form the moulded body. In the known method, the laser is used to write the layer information into the dried green sheet via a sintering process. Laser irradiation certainly causes local sintering of the green sheet, so that irradiated areas can subsequently be detached from the green body using water as the solvent when demoulding, but the laser-irradiated areas possess different properties from conventionally sintered ceramics. Even subsequent conventional sintering cannot influence the properties of the component constructed in this way such that a component with characteristics comparable to a conventionally sintered component is produced.
3D binder printing processes are also known, for example from the document WO 98/09798. In this case, as part of a process in which materials are bonded in layers, a bonding agent is activated after a layer of powder or granulate has been applied. The bonding agent serves as an adhesive for the layers that are applied in steps. Materials suitable for this purpose are described in document DE 10 2006 029 298 A1, for example.